<?php
/**
 * Class used internally by Diff to actually compute the diffs.
 *
 * This class uses the xdiff PECL package (http://pecl.php.net/package/xdiff)
 * to compute the differences between the two input arrays.
 *
 * $Horde: framework/Text_Diff/Diff/Engine/xdiff.php,v 1.4.2.3 2008/01/04 10:37:27 jan Exp $
 *
 * Copyright 2004-2008 The Horde Project (http://www.horde.org/)
 *
 * See the enclosed file COPYING for license information (LGPL). If you did
 * not receive this file, see http://opensource.org/licenses/lgpl-license.php.
 *
 * @author  Jon Parise <jon@horde.org>
 * @package Text_Diff
 */
class Text_Diff_Engine_xdiff {

	/**
	 */
	function diff($from_lines, $to_lines)
	{
		array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
		array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

		/* Convert the two input arrays into strings for xdiff processing. */
		$from_string = implode("\n", $from_lines);
		$to_string = implode("\n", $to_lines);

		/* Diff the two strings and convert the result to an array. */
		$diff = xdiff_string_diff($from_string, $to_string, count($to_lines));
		$diff = explode("\n", $diff);

		/* Walk through the diff one line at a time.  We build the $edits
		 * array of diff operations by reading the first character of the
		 * xdiff output (which is in the "unified diff" format).
		 *
		 * Note that we don't have enough information to detect "changed"
		 * lines using this approach, so we can't add Text_Diff_Op_changed
		 * instances to the $edits array.  The result is still perfectly
		 * valid, albeit a little less descriptive and efficient. */
		$edits = array();
		foreach ($diff as $line) {
			switch ($line[0]) {
				case ' ':
					$edits[] = new Text_Diff_Op_copy(array(substr($line, 1)));
					break;

				case '+':
					$edits[] = new Text_Diff_Op_add(array(substr($line, 1)));
					break;

				case '-':
					$edits[] = new Text_Diff_Op_delete(array(substr($line, 1)));
					break;
			}
		}

		return $edits;
	}

}
